Antitumoral carbazoles

ABSTRACT

The invention provides a compound of formula (I). This invention relates to heterocyclic compounds. It further relates to methods for their preparation, compositions cotaining them and their use as a medicament, particularly as a medicament for the treatment and prophylaxis of cancer.

FIELD OF THE INVENTION

This invention relates to heterocyclic compounds. It further relates tomethods for their preparation, compositions containing them and theiruse as a medicament, particularly as a medicament for the treatment andprophylaxis of cancer.

DESCRIPTION OF THE PRIOR ART

The compounds believed to be closest in structure to those of thepresent invention are carbazomycins G and H [compounds (A) and (B)],which were isolated from the culture broth of Streptoverticilliumehimense in 1988: see Kaneda, et al., J. Antibiot. 1988, 41, 603.Carbazomycin G was found to have some antimicrobial properties and thetotal synthesis of carbazomycins G and H has been reported: see Knölker,et al. Tetrahedron Lett. 1997, 38, 4051.

Another compound close in structure to the compounds of the presentinvention is the plant alkaloid ellipticine (C). This compound is wellknown for its cytostatic activity: see for example Dalton et al. Aust J.Chem. 1967, 20, 2715; Svoboda et al. J. Pharm. Sci. 1968, 57, 1720.

Carba analogues of (C) have been synthesized resuming in an analogue,compound (D): see Boogaard, A. T.; Pandit, U. K.; Koomen, G-J.Tetrahedron. 1994, 50, 4811. This compound has structural similaritieswith the compounds of the present invention.

The structure of each of these compounds is shown on the following page.

SUMMARY OF THE INVENTION

The compounds of the present invention possess a distinctivefunctionality in that the central ring nitrogen atom is bonded directlyto an oxygen atom. Compounds of this type having such a functional grouphave not previously been disclosed in the prior art.

Furthermore, certain preferred compounds of the present inventionpossess alkanoyl (particularly formyl) and hydroxyl substituents on thesame ring carbon atoms.

Thus, in a first aspect, the invention provides compounds of formula(I):

wherein:

the dotted line represents an optional double bond, with the provisothat at least one single bond is present between C7 and C10;

-   R¹ is selected from hydrogen, C₁₋₁₂ alkyl (which may be optionally    substituted by a group selected from hydroxy, C₁₋₁₂ alkoxy, C₁₋₃₀    alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy, optionally    substituted C₈₋₁₆ aralkanoyloxy, halogen, optionally substituted    C₆₋₁₀ aryl, amino, mono-(C₁₋₁₂ alkyl)amino and di-(C₁₋₁₂    alkyl)amino), optionally substituted C₆₋₁₀ aryl, carboxy, C₁₋₃₀    alkoxycarbonyl, optionally substituted C₇₋₁₁ aryloxycarbonyl,    optionally substituted C₈₋₁₆ aralkyloxycarbonyl, carbamoyl, N—(C₁₋₁₂    alkyl)carbamoyl and N,N-di-(C₁₋₁₂ alkyl)carbamoyl;-   R^(2a) and R^(2b) are independently selected from hydrogen, hydroxy,    C₁₋₁₂ alkyl, C₁₋₃₀ alkanoyl, optionally substituted C₇₋₁₁ aroyl,    optionally substituted C₈₋₁₆ aralkanoyl, C₁₋₁₂ alkoxy, C₁₋₃₀    alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy and optionally    substituted C₈₋₁₆ aralkanoyloxy, with the proviso that the    substituent R^(2b) is absent if a double bond is present between C7    and C8;-   or R^(2a) and R^(2b) together represent oxygen;-   R^(3a) and R^(3b) are independently selected from hydrogen, halogen,    hydroxy, amino, mono-(C₁₋₁₂ alkyl)amino, di-(C₁₋₁₂ alkyl)amino,    C₁₋₁₂ alkoxy, C₁₋₃₀ alkanoyloxy, optionally substituted C₇₋₁₁    aroyloxy, optionally substituted C8–16 aralkanoyloxy, C₁₋₁₂ alkyl    (which may be optionally substituted by a group selected from    hydroxy, C₁₋₁₂ alkoxy, C₁₋₃₀ alkanoyloxy, optionally substituted    C₇₋₁₁ aroyloxy, optionally substituted C₈₋₁₆ aralkanoyloxy, halogen,    optionally substituted C₆₋₁₀ aryl, amino, mono-(C₁₋₁₂ alkyl)amino    and di-(C₁₋₁₂ alkyl)amino), optionally substituted C₆₋₁₀ aryl, C₁₋₃₀    alkanoyl, optionally substituted C₇₋₁₁ aroyl, optionally substituted    C₈₋₁₆ aralkanoyl, carboxy, C₁₋₃₀ alkoxycarbonyl, optionally    substituted C₇₋₁₁ aryloxycarbonyl, optionally substituted C₈₋₁₆    aralkyloxycarbonyl, carbamoyl, N—(C₁₋₁₂ alkyl)carbamoyl and    N,N-di-(C₁₋₁₂ alkyl)carbamoyl, with the proviso that the substituent    R^(3b) is absent if a double bond is present between C9 and C10;-   or R^(3a) and R^(3b) together represent oxygen; and-   R⁴ is selected from hydrogen, C₁₋₁₂ alkyl, C₁₋₃₀ alkanoyl,    optionally substituted C₇₋₁₁ aroyl and optionally substituted C₈₋₁₆    aralkanoyl;    and pharmaceutically acceptable salts thereof.

Compounds of formula (I) exhibit antitumoral activity. As describedbelow, the compounds exhibit activity against a wide range of mammaliancancer cell lines.

Thus, in further aspects, the invention provides the use of a compoundof formula (I) or a pharmaceutically acceptable salt thereof as amedicament, particularly the use of such a compound in the manufactureof a medicament for the treatment and prophylaxis of cancer (inparticular lung cancer, prostate cancer, colon cancer and melanoma).

The invention further provides a method for the treatment or prophylaxisof cancer (in particular lung cancer, prostate cancer, colon cancer andmelanoma) in a mammal (in particular a human), comprising administeringto the affected individual an effective amount of a compound of formula(I) or a pharmaceutically acceptable salt thereof.

The invention further provides a method of production of a compound offormula (I), described in more detail later.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the definitions used in the present application, alkyl groups may bestraight or branched chain groups and preferably have from 1 to about 12carbon atoms, more preferably 1 to about 8 carbon atoms, still morepreferably 1 to about 6 carbon atoms, and most preferably 1, 2, 3 or 4carbon atoms. Methyl, ethyl and propyl including isopropyl areparticularly preferred alkyl groups in the compounds of the presentinvention. As used herein, the term alkyl, unless otherwise modified,refers to both cyclic and noncyclic groups, although cyclic groups willcomprise at least three carbon ring members.

The alkyl groups in the compounds of the present invention may besubstituted by a number of different groups, including hydroxy, alkoxy,alkanoyloxy, aroyloxy, aralkanoyloxy, aryl, halogen, amino,monoalkylamino and dialkylamino. These groups are defined in more detailbelow. The number of substituents on the alkyl group is restricted onlyby the number of substitutable positions and by steric constraints.However, we prefer that the alkyl groups have from 1 to 3, morepreferably 1 or 2, and most preferably only 1 substituent. When thesubstituted alkyl group is bonded to a ring, we prefer that thesubstituent is present on the carbon atom attached to the ring.

The aryl groups in the compounds of the present invention preferablyhave 6 to 10 carbon atoms in a single aromatic carbocyclic ring or twoor more fused rings. Phenyl and naphthyl groups, especially the phenylgroup, are preferred.

The aryl groups may optionally be substituted on the aromatic ring byone or more substituents. When more than one substituent is present, thesubstituents may be the same or different. The number of substituents onthe aryl group is restricted only by the number of substitutablepositions and by steric constraints. However, we prefer that the alkylgroups have from 1 to 5, more preferably 1 to 3, still more preferably 1or 2, and most preferably only 1 substituent. The substituents mayinclude alkyl, hydroxy, alkoxy, alkanoyloxy, aroyloxy, aralkanoyloxy,aryl, halogen, amino, monoalkylamino, dialkylamino, nitro and cyanogroups, which are defined in more detail elsewhere in thisspecification.

Preferred aralkyl groups in the compounds of the present inventioncomprise an alkyl group having from 1 to 6 carbon atoms which issubstituted with an aryl group as defined above to form an aralkyl grouphaving a total of 7 to 16 carbon atoms. The aryl part of the aralkylgroup may optionally be substituted on the aromatic ring by one or moresubstituents, the number and type of which is described above inrelation to aryl groups. Examples of preferred alkyl groups includebenzyl, phenethyl, phenylpropyl, 1-naphthylmethyl and naphthylethyl, ofwhich the benzyl group is most preferred.

The halogen atoms in the compounds of the present invention arepreferably fluorine, chlorine, bromine or iodine, of which chlorine andbromine are more preferred.

Preferred alkoxy groups in the compounds of the present inventioninclude groups having one or more (but preferably only one) oxygenlinkages and from 1 to about 12 carbon atoms, more preferably from 1 toabout 8 carbon atoms, and still more preferably 1 to about 6 carbonatoms, and most preferably 1, 2, 3 or 4 carbon atoms. Preferred alkanoylgroups in the compounds of the present invention include those groupshaving one or more carbonyl (CO) groups and from 1 to about 30 carbonatoms, more preferably from 1 to about 12 carbon atoms, and still morepreferably 1 to about 6 carbon atoms (including the carbonyl carbon).Alkanoyl groups having 1, 2, 3 or 4 carbon atoms, especially the formyl,acetyl, propionyl, butyryl and isobutyryl groups, are preferred and theformyl and acetyl groups especially preferred.

Preferred aroyl groups in the compounds of the present invention includethose groups having one or more (but preferably only one) carbonyl (CO)groups bonded to an aryl group (defined above) to complete an aroylgroup having a total of from 7 to 11 carbon atoms. The aryl part of thearoyl group may optionally be substituted by one or more substituents,the preferred number and type of which is described above in relation toaryl groups. Examples of preferred aroyl groups include benzoyl andnaphthoyl, of which the benzoyl group is most preferred.

Preferred aralkanoyl groups in the compounds of the present inventioninclude those groups having one or more (but preferably only one)carbonyl (CO) groups bonded to the alkyl part of an aralkyl group(defined above) to complete an aralkanoyl group having a total of from 8to 16 carbon atoms. The aryl part of the aralkanoyl group may optionallybe substituted by one or more substituents, the preferred number andtype of which is described above in relation to aryl groups. Examples ofpreferred aralkanoyl groups include phenylacetyl, 3-phenylpropionyl,4-phenylbutyryl and naphthylacetyl, of which the phenylacetyl group ismost preferred.

Preferred alkanoyloxy groups in the compounds of the present inventioninclude those groups having one or more carbonyloxy groups and from 1 toabout 30 carbon atoms, more preferably from 1 to about 12 carbon atoms,and still more preferably 1 to about 6 carbon atoms (including thecarbonyl carbon). When the term “alkanoyloxy” is used, it is to beunderstood that the group is attached to the rest of the molecule viathe oxygen atom. Alkanoyloxy groups having 1, 2, 3 or 4 carbon atoms,especially the formyloxy, acetoxy, propionyloxy, butyryloxy andisobutyryloxy groups, are preferred and the formyloxy and acetyloxygroups especially preferred.

Preferred aroyloxy groups in the compounds of the present inventioninclude those groups having one or more (but preferably only one)carbonyloxy (COO) groups wherein the carbonyl carbon is bonded to anaryl group (defined above) and the oxygen atom is attached to theremainder of the molecule. The aroyloxy group preferably has a total offrom 7 to 11 carbon atoms (including the carbonyl carbon). The aryl partof the aroyloxy group may optionally be substituted by one or moresubstituents, the preferred number and type of which is described abovein relation to aryl groups. Examples of preferred aroyloxy groupsinclude benzoyloxy and naphthoyloxy, of which the benzoyloxy group ismost preferred.

Preferred aralkanoyloxy groups in the compounds of the present inventioninclude those groups having one or more (but preferably only one)carbonyloxy (COO) groups wherein the carbonyl carbon is bonded to thealkyl part of an aralkyl group (defined above) and the oxygen atom isattached to the remainder of the molecule. The aralkanoyloxy group has atotal of from 8 to 16 carbon atoms (including the carbonyl carbon). Thearyl part of the aralkanoyloxy group may optionally be substituted byone or more substituents, the preferred number and type of which isdescribed above in relation to aryl groups. Examples of preferredaralkanoyloxy groups include phenylacetoxy, 3-phenylpropionyloxy,4-phenylbutyryloxy and naphthylacetoxy, of which the phenylacetoxy groupis most preferred.

Preferred N-alkylcarbamoyl groups in the compounds of the presentinvention comprise a —CO—NH— linkage (the group being attached to therest of the molecule via the carbonyl carbon) wherein the nitrogen atomis substituted with an alkyl group having from 1 to about 12 carbonatoms, more preferably 1 to about 6 carbon atoms. N-Alkylcarbamoylgroups having 1, 2, 3 or 4 carbon atoms, especially theN-methylcarbamoyl, N-ethylcarbamoyl, N-propylcarbamoyl andN-butylcarbamoyl groups, are particularly preferred.

Preferred dialkylcarbamoyl groups in the compounds of the presentinvention comprise a —CO—N— linkage (the group being attached to therest of the molecule via the carbonyl carbon) wherein the nitrogen atomis substituted with two alkyl groups, each having from 1 to about 12carbon atoms, more preferably 1 to about 6 carbon atoms. The alkylgroups may be the same or different. N,N-Dialkylcarbamoyl groups whereineach alkyl group has 1, 2, 3 or 4 carbon atoms, especially theN,N-dimethylcarbamoyl, N,N-diethylcarbamoyl, N-methyl-N-ethylcarbamoyl,N-ethyl-N-propylcarbamoyl, N,N-dipropylcarbamoyl, N,N-dibutylcarbamoyland N-methyl-N-butylcarbamoyl groups, are particularly preferred.

Preferred monoalkylamino groups in the compounds of the presentinvention have one or more (but preferably only one) NH linkages andfrom 1 to about 12 carbon atoms, more preferably from 1 to about 8carbon atoms, and still more preferably 1 to about 6 carbon atoms.Alkylamino groups having 1, 2, 3 or 4 carbon atoms, especially themethylamino, ethylamino, propylamino and butylamino groups, areparticularly preferred.

Preferred dialkylamino groups in the compounds of the present inventionhave one or more (but preferably only one) nitrogen atom bonded to twoalkyl groups, each of which may from 1 to about 12 carbon atoms, morepreferably from 1 to about 8 carbon atoms, and still more preferably 1to about 6 carbon atoms. The alkyl groups may be the same or different.Dialkylamino groups wherein each alkyl group has 1, 2, 3 or 4 carbonatoms, especially the dimethylamino, diethylamino, N-methylethylamino,N-ethylpropylamino, dipropylamino, dibutylamino and N-methylbutylaminogroups, are particularly preferred.

Preferred alkoxycarbonyl groups in the compounds of the presentinvention include those groups having one or more (but preferably onlyone) oxycarbonyl groups and from 1 to about 30 carbon atoms, morepreferably from 1 to about 12 carbon atoms, and still more preferably 1to about 6 carbon atoms (including the carbonyl carbon). When the term“alkoxycarbonyl”is used, it is to be understood that the group isattached to the rest of the molecule via the carbonyl carbon.Alkoxycarbonyl groups having 1, 2, 3 or 4 carbon atoms, especially themethoxycarbonyl, ethoxycarbonyl, propoxycarbonyl and butoxycarbonyl arepreferred and the methoxycarbonyl and ethoxycarbonyl groups especiallypreferred.

Preferred aryloxycarbonyl groups in the compounds of the presentinvention have one or more (but preferably only one) oxycarbonyl groupswherein the carbonyl carbon is attached to the rest of the molecule andthe oxygen atom is bonded to an aryl group (as defined above). Thearyloxycarbonyl group preferably has a total of from 7 to 11 carbonatoms (including the carbonyl carbon). The aryl part of thearyloxycarbonyl group may optionally be substituted by one or moresubstituents, the preferred number and type of which is described abovein relation to aryl groups. Examples of preferred aryloxycarbonyl groupsinclude phenoxycarbonyl and naphthyloxycarbonyl, of which thephenoxycarbonyl group is most preferred.

Preferred aralkyloxycarbonyl groups in the compounds of the presentinvention have one or more (but preferably only one) oxycarbonyl groupswherein the carbonyl carbon is attached to the rest of the molecule andthe oxygen atom is bonded to the alkyl part of an aralkyl group (definedabove). The aralkyloxycarbonyl group has a total of from 8 to 16 carbonatoms (including the carbonyl carbon). The aryl part of thearalkyloxycarbonyl group may optionally be substituted by one or moresubstituents, the preferred number and type of which is described abovein relation to aryl groups. Examples of preferred aralkyloxycarbonylgroups include benzyloxycarbonyl, phenethyloxycarbonyl andnaphthylmethyloxycarbonyl, of which the benzyloxycarbonyl group is mostpreferred.

Preferably R¹ is selected from carboxy, C₁₋₁₂ alkoxycarbonyl, carbamoyl,N—(C₁₋₆ alkyl)carbamoyl and N,N-di-(C₁₋₆ alkyl)carbamoyl. Morepreferably, R¹ is selected from carboxy and C₁₋₆ alkoxycarbonyl. Stillmore preferably, R¹ is C₁₋₄ alkoxycarbonyl. In a particularly preferredembodiment, R¹ is methoxycarbonyl.

Preferably R^(2a) and R^(2b) are independently selected from hydrogen,hydroxy, C₁₋₆ alkoxy and C₁₋₁₂ alkanoyloxy, or R^(2a) and R^(2b)together represent oxygen. More preferably, R^(2a) and R^(2b) areindependently selected from hydrogen, hydroxy and C₁₋₄ alkoxy, or R^(2a)and R^(2b) together represent oxygen. It is particularly preferred thatR^(2a) and R^(2b) together represent oxygen.

Preferably R^(3a) and R^(3b) are independently selected from hydrogen,hydroxy, C₁₋₆ alkoxy, C₁₋₁₂ alkanoyloxy, C₁₋₆ alkyl (which may beoptionally substituted by a group selected from hydroxy, C₁₋₆ alkoxy andC₁₋₁₂ alkanoyloxy), C₁₋₁₂ alkanoyl, carboxy and C₁₋₁₂ alkoxycarbonyl; orR^(3a) and R^(3b) together represent oxygen. More preferably, R^(3a) andR^(3b) are independently selected from hydrogen, hydroxy, C₁₋₄ alkyl(which is substituted by a group selected from hydroxy and C₁₋₄ alkoxy),C₁₋₆ alkanoyl, carboxy and C₁₋₆ alkoxycarbonyl. Even more preferably,R^(3a) and R^(3b) are independently selected from hydroxy,hydroxymethyl, C₁₋₄ alkanoyl and carboxy. It is particularly preferredthat one of R^(3a) and R^(3b) is hydroxy and the other is formyl.

It is preferred that a double bond is present between C8 and C9.However, in alternative embodiments, double bonds are present between C7and C8 and between C9 and C10 (so as to make the ring including C7, C8,C9 and C10 aromatic).

As the person skilled in the art will readily appreciate, the preferreddefinitions of R¹, R², R³, R⁴ and the dotted line may be combined invarious ways, and the compounds covered by all such combinations andpermutations of the above preferred definitions are to be considered asbeing part of this invention. A combination of two preferred definitionsis more preferred, a combination of three preferred definitions is evenmore preferred, a combination of four preferred definitions is stillmore preferred and a combination of all five preferred definitions isespecially preferred.

The most preferred compound of this invention is8-formyl-8,9-dihydroxy-5-oxo-8,9-dihydro-5H-carbazole-1-carboxylic acidmethyl ester (coproverdine).

Some of the compounds of formula (I) contain a basic group (such as anamino group), and may therefore form a salt. The nature of such salts isnot critical to the present invention, provided that, when the compoundis used for therapeutic purposes, the salts are pharmaceuticallyacceptable, ie more pharmaceutically active, about as pharmaceuticallyactive or not unduly less pharmaceutically active than the free basecompound, and less toxic, about as toxic or not unduly more toxic thanthe free base compound. This can easily be ascertained by simple testsreadily apparent to those skilled in the art. However, when the compoundis used for other purposes (for example, as an intermediate in thepreparation of another compound) even this restriction does not apply.Examples of suitable salts include inorganic acid salts such ashydrofluoride, hydrochloride, hydrobromide, hydroiodide, sulfate andphosphate; carboxylic acid salts such as acetate, benzoate, oxalate,maleate, fumarate, tartrate, citrate and succinate; and sulfonic acidsalts such as methanesulfonate, benzenesulfonate and p-toluenesulfonate.Preferred salts include hydrochloride, hydrobromide, tartrate andsuccinate.

Some of the compounds of formula (I) have acidic groups, such as aphenolic hydroxyl group or a carboxy group, and may therefore form asalt by combination with a metal ion. The nature of such salts is notcritical to the present invention, provided that, when the compound isused for therapeutic purposes, the salts are pharmaceuticallyacceptable, ie more pharmaceutically active, about as pharmaceuticallyactive or not unduly less pharmaceutically active than the free acidcompound, and less toxic, about as toxic or not unduly more toxic thanthe free acid compound. This can easily be ascertained by simple testsreadily apparent to those skilled in the art. However, when the compoundis used for other purposes (for example, as an intermediate in thepreparation of another compound) even this restriction does not apply. Asalt of such a compound can be prepared by a conventional method.Examples of the salt include alkali metal salts such as lithium, sodiumand potassium salts; alkaline earth metal salts such as calcium, bariumand magnesium salts; salts of other metals such as an aluminium and ironsalts; ammonium salts; and organic amine salts such as methylamine andtriethylamine salts.

Certain compounds of formula (I) have asymmetric carbon atoms, anddifferent stereoisomers (both enantiomers and diastereomers) of suchcompounds can therefore exist. The present invention encompasses eachpure stereoisomer and a mixture of the isomers in any ratio. A pureenantiomer of the compound of formula (I) can, for example, besynthesized from an optically active starting material or can beobtained from a mixture of enantiomers of compounds of formula (I) via aconventional optical resolution technique.

The most preferred compound of the present invention (coproverdine) maybe prepared by isolating it from a natural source, in particular from anascidian. Conveniently, the compound may be isolated by extraction usinga suitable solvent. The solvent may preferably be an organic solvent:for example, an aliphatic hydrocarbon such as hexane, heptane, ligroinor petroleum ether; an aromatic hydrocarbon such as benzene, toluene orxylene; a halogeno-hydrocarbon such as dichloromethane, chloroform,carbon tetrachloride, dichloroethane, chlorobenzene or dichlorobenzene;an ether such as diethyl ether, diisopropyl ether, tetrahydrofuran,dioxane, dimethoxyethane or diethylene glycol dimethyl ether; an alcoholsuch as methanol, ethanol or isopropanol; a ketone such as acetone,methyl ethyl ketone, methyl isobutyl ketone, isophorone orcyclohexanone; an amide such as formamide, dimethylformamide,dimethylacetamide, N-methyl-2-pyrrolidone or hexamethylphosphorictriamide; a sulfoxide such as dimethylsulfoxide; or a sulfone such assulfolane; or mixtures thereof. The solvent is preferably a mixture ofdichloromethane and methanol.

The compound may then be further purified by purification techniquesknown to those skilled in the art, for example recrystallisation (forsolid compounds) or chromatographic techniques such as columnchromatography, liquid chromatography or gas chromatography, inparticular liquid chromatography techniques such as reversed-phaseliquid chromatography, vacuum liquid chromatography and/or gelpermeation chromatography.

The compounds of the present invention other than coproverdine may beprepared by derivatising coproverdine. The compound may undergo multipletransformations to produce a wide range of possible derivatives. Thenature of such derivatisations will be readily apparent to those skilledin the art.

For example, a compound of formula (I) wherein R¹ is a carboxy group maybe prepared from coproverdine by hydrolysis of the methyl ester group.The hydrolysis may be catalysed by acid or base and may be achieved, forexample, by treating coproverdine with aqueous acid or base, for exampleaqueous hydrochloric acid or aqueous sodium hydroxide.

A compound of formula (I) wherein R¹ is an alkoxycarbonyl group (otherthan a methoxycarbonyl group), an aryloxycarbonyl group or anaralkyloxycarbonyl group may be prepared from coproverdine byreplacement of the methyl ester group with an alternative ester group.This may conveniently be achieved by treating coproverdine with asuitable alcohol or alkoxide derivative in a transesterificationreaction. The transesterification reaction may preferably be catalysedby acid or base.

Similarly, a compound of formula (I) wherein R¹ is a carbamoyl,monoalkylcarbamoyl or dialkylcarbamoyl group may be prepared fromcoproverdine by replacement of the methyl ester group with an amidegroup. Such a transformation may be achieved, for example, by treatingcoproverdine with ammonia, a suitable mono- or dialkylamine or a saltthereof.

A compound of formula (I) wherein R¹ is a hydroxymethyl group may beprepared from coproverdine (or from a compound wherein R¹ is anotheralkoxycarbonyl group, an aryloxycarbonyl group or an aralkyloxycarbonylgroup) by reduction of the ester group. Any suitable agent known in theart to reduce esters may be used, examples of which include lithiumaluminium hydride, diisobutylaluminium hydride, borane andtriethoxysilane.

Similarly, a compound of formula (I) wherein R¹ is an alkyl groupsubstituted at the carbon next to the ring with a monoalkylamino ordialkylamino group may be prepared from such a compound wherein R¹ is acarbamoyl, monoalkylcarbamoyl or dialkylcarbamoyl group by reduction ofthe amide group. Any suitable agent known in the art to reduce amidesmay be used, examples of which include lithium aluminium hydride, boraneand trichlorosilane.

A compound of formula (I) wherein one of R^(2a) and R^(2b) is hydrogenand the other is hydroxy may conveniently be prepared from coproverdineby reduction of the ketone group. Any suitable agent known in the art toreduce a ketone group may be used, examples of which include lithiumaluminium hydride, diisobutylaluminium hydride, sodium borohydride,sodium cyanoborohydride, borane, tributyltin hydride, lithiumtrimethoxyaluminium hydride, hydrogen and a metal catalyst (preferablyplatinum) and aluminium triisopropoxide in isopropanol.

A compound of formula (I) wherein one of R^(2a) and R^(2b) is hydrogenand the other is alkoxy may conveniently be prepared from a compoundwherein one of R^(2a) and R^(2b) is hydrogen and the other is hydroxy byalkylation of the hydroxy group (or its conjugate base) with a suitablealkylating agent. Any suitable alkylating agent may be used, examples ofwhich include alkyl halides such as methyl bromide and methyl iodide,alkyl sulfates such as dimethyl sulfate, and alkylsulfonates such aspropyl p-toluenesulfonate and ethyl trifluoromethanesulfonate. Thereaction may preferably be catalysed by a suitable base, examples ofwhich include organic bases such as pyridine, N,N-dimethylaminopyridineand triethylamine and inorganic bases such as sodium hydroxide, sodiumcarbonate and sodium hydrogen carbonate.

Similarly, a compound of formula (I) wherein one of R^(2a) and R^(2b) ishydrogen and the other is alkanoyloxy, aroyloxy or aralkanoyloxy mayconveniently be prepared from a compound wherein one of R^(2a) andR^(2b) is hydrogen and the other is hydroxy by acylation of the hydroxygroup with a suitable acylating agent. Any suitable acylating agent maybe used, examples of which include acid halides such as acetyl chloride,acid anhydrides such as acetic anhydride and a carboxylic acid (forexample, acetic acid) in the presence of a dehydrating agent such asdicyclohexylcarbodiimide (DCC). The reaction may preferably be catalysedby a suitable base, examples of which include organic bases such aspyridine, N,N-dimethylaminopyridin and triethylamine and inorganic basessuch as sodium hydroxide, sodium carbonate and sodium hydrogencarbonate.

A compound of formula (I) wherein one of R^(3a) and R^(3b) is hydroxyand the other is hydroxymethyl may conveniently be prepared fromcoproverdine by reduction of the formyl group. Any suitable agent knownin the art to reduce a formyl group may be used, examples of whichinclude lithium aluminium hydride, diisobutylaluminium hydride, sodiumborohydride, sodium cyanoborohydride, borane, tributyltin hydride,lithium trimethoxyaluminium hydride, hydrogen and a metal catalyst(preferably platinum) and aluminium triisopropoxide in isopropanol.

A compound of formula (I) wherein one of R^(3a) and R^(3b) is methylsubstituted with an alkoxy group may be prepared from a compound whereinone of R^(3a) and R^(3b) is hydroxymethyl by alkylation of the hydroxygroup (or its conjugate base) with a suitable alkylating agent. Anysuitable alkylating agent may be used, examples of which are describedand exemplified above in relation to the transformations involving thegroups R^(2a) and R^(2b). The reaction may preferably be catalysed by asuitable base, examples of which are described and exemplified above inrelation to the transformations involving the groups R^(2a) and R^(2b).

Similarly, a compound of formula (I) wherein one of R^(3a) and R^(3b) ismethyl substituted with an alkanoyloxy, aroyloxy or aralkanoyloxy groupmay be prepared from a compound wherein one of R^(3a) and R^(3b) ishydroxymethyl by acylation of the hydroxy group (or its conjugate base)with a suitable acylating agent. Any suitable acylating agent may beused, examples of which are described and exemplified above in relationto the transformations involving the groups R^(2a) and R^(2b). Thereaction may preferably be catalysed by a suitable base, examples ofwhich include organic bases such as pyridine, N,N-dimethylaminopyridineand triethylamine and inorganic bases such as sodium hydroxide, sodiumcarbonate and sodium hydrogen carbonate.

A compound of formula (I) wherein one of R^(3a) and R^(3b) is carboxymay be conveniently be prepared from coproverdine by oxidation of theformyl group. Any agent suitable for oxidising an aldehyde group may beemployed, examples of which include potassium dichromate, chromiumtrioxide in sulfuric acid, nitric acid and potassium permanganate.

A compound of formula (I) wherein one of R^(3a) and R^(3b) is analkoxycarbonyl group, an aryloxycarbonyl group or an aralkyloxycarbonylgroup may be prepared from a compound wherein one of R^(3a) and R^(3b)is carboxy by esterification of the carboxylic acid group. This may beachieved by any convenient means known in the art. For example, thestarting compound may be treated directly with a suitable alcohol in thepresence of acid. Alternatively the carboxy group may first be convertedto a more reactive derivative (such as an acid halide or acid anhydride)by treatment with a suitable reagent, eg oxalyl chloride, phosphorustrichloride or acetic anhydride, followed by treatment with a suitablealcohol. The reaction(s) may preferably be catalysed by a suitable base,examples of which are described and exemplified above in relation to thetransformations involving the groups R^(2a) and R^(2b).

Similarly, a compound of formula (I) wherein one of R^(3a) and R^(3b) isa carbamoyl, monoalkylcarbamoyl or dialkylcarbamoyl group may beprepared from a compound of formula (I) wherein one of R^(3a) and R^(3b)is carboxy by treating the starting compound with ammonia, a suitablemono- or dialkylamine or a salt thereof. The compound may be treateddirectly with the starting reagent or the carboxy group may first beconverted to a more reactive derivative as described above.

A compound of formula (I) wherein R⁴ is alkyl may conveniently beprepared from coproverdine by alkylation of the hydroxy group (or itsconjugate base) with a suitable alkylating agent. Any suitablealkylating agent may be used, examples of which are described andexemplified above in relation to the transformations involving thegroups R^(2a) and R^(2b). The reaction may preferably be catalysed by asuitable base, examples of which are described and exemplified above inrelation to the transformations involving the groups R^(2a) and R^(2b).

Similarly, a compound of formula (I) wherein R⁴ is alkanoyl, aroyl oraralkanoyl may conveniently be prepared from coproverdine by acylationof the hydroxy group with a suitable acylating agent. Any suitableacylating agent may be used, examples of which are described andexemplified above in relation to the transformations involving thegroups R^(2a) and R^(2b). The reaction may preferably be catalysed by asuitable base, examples of which include organic bases such as pyridine,N,N-dimethylaminopyridine and triethylamine and inorganic bases such assodium hydroxide, sodium carbonate and sodium hydrogen carbonate.

When coproverdine is treated with certain reducing agents, both the oxogroup R^(2a)/R^(2b) and the formyl group R^(3b) may be simultaneouslyreduced to give a compound wherein R^(2a) is hydrogen, R^(2b) is hydroxyand R^(3b) is a hydroxymethyl group.

When coproverdine is reduced to give a compound wherein one of R^(2a)and R^(2b) is hydrogen and one of R^(3a) and R^(3b) is hydroxy, thecompound may lose a molecule of water to form a compound wherein doublebonds are present between C7 and C8 and between C9 and C10. An exampleof this process is shown below:

The present invention also relates to pharmaceutical preparations, whichcontain as active ingredient a compound or compounds of the invention,as well as the processes for their preparation.

Examples of pharmaceutical compositions include any solid (tablets,pills, capsules, granules, etc.) or liquid (solutions, suspensions oremulsions) with suitable composition or oral, topical or parenteraladministration, and they may contain the pure compound or in combinationwith any carrier or other pharmacologically active compounds. Thesecompositions may need to be sterile when administered parenterally.

Administration of the compounds or compositions of the present inventionmay be by any suitable method, such as intravenous infusion, oralpreparations, intraperitoneal and intravenous administration. We preferthat infusion times of up to 24 hours are used, more preferably 2–12hours, with 2–6 hours most preferred. Short infusion times which allowtreatment to be carried out without an overnight stay in hospital areespecially desirable. However, infusion may be 12 to 24 hours or evenlonger if required. Infusion may be carried out at suitable intervals ofsay 2 to 4 weeks. Pharmaceutical compositions containing compounds ofthe invention may be delivered by liposome or nanosphere encapsulation,in sustained release formulations or by other standard delivery means.

The correct dosage of the compounds will vary according to theparticular formulation, the mode of application, and the particularsitus, host and tumour being treated. Other factors like age, bodyweight, sex, diet, time of administration, rate of excretion, conditionof the host, drug combinations, reaction sensitivities and severity ofthe disease shall be taken into account. Administration can be carriedout continuously or periodically within the maximum tolerated dose.

The compounds and compositions of this invention may be used with otherdrugs to provide a combination therapy. The other drugs may form part ofthe same composition, or be provided as a separate composition foradministration at the same time or a different time. The identity of theother drug is not particularly limited, and suitable candidates include:

-   a) drugs with antimitotic effects, especially those which target    cytoskeletal elements, including microtubule modulators such as    taxane drugs (such as taxol, paclitaxel, taxotere, docetaxel),    podophylotoxins or vinca alkaloids (vincristine, vinblastine);-   b) antimetabolite drugs such as 5-fluorouracil, cytarabine,    gemcitabine, purine analogues such as pentostatin, methotrexate);-   c) alkylating agents such as nitrogen mustards (such as    cyclophosphamide or ifosphamide);-   d) drugs which target DNA such as the antracycline drugs adriamycin,    doxorubicin, pharmorubicin or epirubicin;-   e) drugs which target topoisomerases such as etoposide;-   f) hormones and hormone agonists or antagonists such as estrogens,    antiestrogens (tamoxifen and related compounds) and androgens,    flutamide, leuprorelin, goserelin, cyprotrone or octreotide;-   g) drugs which target signal transduction in tumour cells including    antibody derivatives such as herceptin;-   h) alkylating drugs such as platinum drugs (cis-platin,    carbonplatin, oxaliplatin, paraplatin) or nitrosoureas;-   i) drugs potentially affecting metastasis of tumours such as matrix    metalloproteinase inhibitors;-   j) gene therapy and antisense agents;-   k) antibody therapeutics;-   l) other bioactive compounds of marine origin, notably the did mnins    such as aplidine;-   m) steroid analogues, in particular dexamethasone;-   n) anti-inflammatory drugs, in particular dexamethasone; and-   o) anti-emetic drugs, in particular dexamethasone.

EXAMPLES

The following Examples illustrate the present invention but do not limitthe scope thereof.

Example 1

8-formyl-8,9-dihydroxy-5-oxo-8,9-dihydro-5H-carbazole-1-carboxylic acidmethyl ester (coproverdine)

A specimen of a rare, unidentified ascidian was collected fromIrishman's Garden at Three Kings (55 km offshore from the Northern tipof the North Island, New Zealand). Collection was by SCUBA at a depth of20–25 m from inside a cave in March 1997. The specimen was described asepizoic on an Anchorina sponge. A voucher specimen is stored in themuseum at NIWA, Wellington, New Zealand (NIWA code MNP670). The specimenis thought to be a polycitorid, possibly a Eudistoma sp.

The frozen specimen (34 g) was exhaustively extracted with MeOH/DCM(3:1; 700 mL), filtered through a pad of Celite® and the extract (1.4 g)subjected to C18 vacuum liquid chromatography, followed by gelpermeation chromatography on Sephadex® LH-20 eluting with MeOH.

The product was further purified using reversed-phase HPLC (4 mL/minflow rate) using a CH₃CN/H₂O gradient (30% to 75%) over 30 minutes on aPhenomenex Prodigy® 5μ ODS column (100 Å; 250×10 mm) with UV detectionat 254 nm to yield the title compound.

Apperance: yellow oil.

Optical rotation [α]²⁰ _(D)−8° (c 0.36, EtOH).

IR spectrum (CHCl₃) ν_(max)/cm⁻¹: 3690 (sharp), 3500 (broad), 1665,1603, 1556, 1290.

UV spectrum (EtOH) λ_(max)/nm (ε) 208 (20000), 270 (6700), 302 (4800),382 (16000)

¹H NMR spectrum (CD₃OD, 300 MHz): See Table 1.

¹³C NMR data (CD₃OD, 75 MHz): See Table 1.

Mass spectrum (EI, 70 eV) m/z 301 (M⁺, 35), 285 (75), 273 (24), 253(48), 225 (100), 213 (28), 197 (26), 169 (28), 146 (20).

High Resolution Fast Atom Bombardment mass spectrum m/z 302.0673 ([MH]⁺,calculated for C₁₅H₁₂NO₆, 302.0665).

TABLE 1 NMR Data for Coproverdine ¹H δ [m, No. ¹³C^(b) J (Hz)]^(c) gCOSYgHMBC^(d) 1 90.5 — — — 2 143.6  7.01 (d, H 3 C1, C4, C9a, C10^(e) J =10.2) 3 128.5  6.25 (d, H 2 C1, C2, C4, C4a, C10^(e) J = 10.2) 4 186.6 —— — 4a 105.7 — — — 4b 127.7 — — — 5 125.1  7.39 (dd, H 6 C4a^(e), C4b,C6, C8a J = 1.5, 8.0) 6 126.4  7.28 (dd, H 5, H 7 C4b, C5, C7, C8, C8a J= 8.0, 8.0) 7 125.9  7.84 (dd, H 6 C4b, C5; C6, C8, C8a^(e), C11 J =1.5, 8.0) 8 118.3 — — — 8a 144.9 — — — 9 — — — — 9a 157.2 — — — 10 192.710.13 (s) — C1, C4a, C9a 11 168.2 — — — 12 53.4  4.06 (s) — C11 1-OH — 8.50 (bs)^(f) — — 9-OH —  8.50 (bs)^(f) — — ^(a)Spectra were recordedin CD₃OD. ^(b13)C NMR at 75 MHz, referenced to CD₃OD (δ 49.3) andassignments are supported by a gHSQC NMR experiment ^(c1)H NMR at 300MHz and 500 MHz, referenced to residual solvent CH₂OD (δ 3.3). ^(d)gHMBCNMR experiments were run using J = 140 and 160 Hz and J_(nxh) = 2, 4, 8,9, 10 Hz. ^(e)These HMBC correlations were weak. ^(f)This signal may beinterchanged.

Example 2

A mixture of coproverdine (0.2 mg) (obtained as described in Example 1above) and NaBH₄ (3.5 mg) in dry methanol (3 mL) were stirred at roomtemperature for 2 hours. The reaction mixture was concentrated underreduced pressure and re-dissolved in methanol (2 mL). The solution wasanalysed by reversed phase HPLC and mass spectrometry. HPLC analysisindicated the presence of two compounds which were more polar thancoproverdine, but with the same UV profile. These compounds are believedto be compounds (2a) and (2b).

Low resolution ESIMS (+ve) (30 V) for compound (2a): m/z 288.21 [MH]⁺;calculated for C₁₅H₁₃NO_(5,): 287.2675.

Biological Activity

Biological tests were carried out on coproverdine (the compound ofExample 1 of the present application). A colorimetric type of assay,using sulforhodamine B (SRB) reaction, was used to provide aquantitative measurement of cell growth and viability. The techniquedescribed by Skehan, et al., J Natl. Cancer Inst., 1990, 82, 1107, wasfollowed. The reader is also referred to the following references:

-   Faircloth et al. Journal of Tissue and Culture Methods, 1988, 11,    201.-   Monks et al. Articles, 1991, 83, 757.-   Mosmann et al. Journal of Immunological Methods, 1983, 65, 55.

The tests gave an IC₅₀ result of 950 ng/mL against th P388 leukemia cellline.

Further biological tests were carried out on coproverdine using similarmethods. The results are given using the following cellular responseparameters: GI=growth inhibition, TGI=total growth inhibition(cytostatic effect) and LC=cell killing (cytotoxic effect).

The results are shown in Table 2 below.

TABLE 2 In vitro AT activity of coproverdine 24 wells/16 mm 96 wells/9mm 10,000 cells/72 h 5,000 cells/48 h Cell lines IC₅₀ (μM) GI₅₀ (μM) TGI(μM) LC₅₀ (μM) Leukemia (P-388) 1.6 nd nd nd Lung (A-549) 0.3 7 15 50Colon (HT-29) 0.3 6 16 50 Melanoma 0.3 nd nd nd (MEL-28) Prostate 0.3 ndnd nd (DU-145) IC₅₀: Concentration that causes 50% growth inhibitionGI₅₀: Concentration that causes 50% growth inhibition with correctionfor cell OD at time zero TGI: Total growth inhibition (cytostaticeffect) LC₅₀: Concentration that causes 50% cell killing (cytotoxiceffect) nd: Not determined

1. A compound of formula (I):

wherein: the dotted line represents an optional double bond, with theproviso that at least one single bond is present between C7 and C10; R¹is selected from hydrogen, C₁₋₁₂ alkyl, which may be optionallysubstituted by a group selected from hydroxyl, C₁₋₁₂ alkoxy, C₁₋₃₀alkanoyloxy, optionally substituted C₇₋₁₁, aroyloxy, optionallysubstituted C₈₋₁₆ aralkanoyloxy, halogen, optionally substituted C₆₋₁₀aryl, amino, mono-(C₁₋₁₂ alkyl)amino and di-(C₁₋₁₂ alkyl)amino;optionally substituted C₆₋₁₀ aryl; carboxy; C₁₋₃₀ alkoxycarbonyl;optionally substituted C₇₋₁₁ aryloxycarbony; optionally substitutedC₈₋₁₆ aralkyloxycarbonyl; carbamoyl; N—(C₁₋₁₂ alkyl)carbamoyl andN,N-di-(C₁₋₁₂ alkyl)carbamoyl; R^(2a) and R^(2b) are independentlyselected from hydrogen, hydroxy, C₁₋₁₂ alkyl, C₁₋₃₀ alkanoyl, optionallysubstituted C₇₋₁₁ aroyl, optionally substituted C₈₋₁₆ aralkanoyl, C₁₋₁₂alkoxy, C₁₋₃₀ alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy andoptionally substituted C₈₋₁₆ aralkanoyloxy, with the proviso that thesubstituent R^(2b) is absent if a double bond is present between C7 andC8; or R^(2a) and R^(2b) together represent oxygen; R^(3a) and R^(3b)are independently selected from hydrogen; halogen; hydroxy; amino;mono-(C₁₋₁₂ alkyl)amino; di-(C₁₋₁₂ alkyl)amino; C₁₋₁₂ alkoxy; C₁₋₃₀alkanoyoxyl; optionally substituted C₇₋₁₁ aroyloxy; optionallysubstituted C₈₋₁₆ aralkanoyloxy; C₁₋₁₂ alkyl, which may be optionallysubstituted by a group selected from hydroxy, C₁₋₁₂ alkoxy, C₁₋₃₀alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy, optionallysubstituted C₈₋₁₆ aralkanoyloxy, halogen, optionally substituted C₆₋₁₀,aryl, amino, mono-(C₁₋₁₂alkyl)amino and di-(C₁₋₁₂ alkyl)amino;optionally substituted C₆₋₁₀ aryl; C₁₋₃₀ alkanoyl, optionallysubstituted C₇₋₁₁ aroyl; optionally substituted C₈₋₁₆ aralkanoyl;carboxy; C₁₋₃₀ alkoxycarbonyl; optionally substituted C₇₋₁₁aryloxycarbonyl; optionally substituted C₈₋₁₆ aralkyloxycarbonyl;carbamoyl; N—(C₁₋₁₂ alkyl) carbamoyl and N,N-di-(C₁₋₁₂ alkyl) carbamoyl,with the proviso that the substituent R^(3b) is absent if a double bondis present between C9 and C10; or R^(3a) and R^(3b) together representoxygen; and R⁴ is selected from hydrogen, unsubstituted C₁₋₁₂ alkyl,C₁₋₃₀ alkanoyl, optionally substituted C₇₋₁₁ aroyl and optionallysubstituted C₈₋₁₆ aralkanoyl; or a pharmaceutically acceptable saltthereof, with the exception of the following compounds: (a) a compoundwherein R¹ is hydrogen or halogen, R^(2a), R^(2b), R^(3a) and R^(3b) areall hydrogen, R⁴ is hydrogen or lower alkyl, and double bonds arepresent between C7 and C8 and between C9 and C10; (b) a compound whereinR¹, R^(2a), R^(2b), R^(3a) and R^(3b) are all hydrogen, R⁴ is methyl,and double bonds are present between C7 and C8 and between C9 and C10;and (c) a compound wherein R¹, R^(2a), R^(2b), R^(3a), R^(3b) and R⁴ areall hydrogen, and no double bonds are present between C7 and C10.
 2. Acompound according to claim 1, wherein R¹ is selected from carboxy,C₁₋₁₂ alkoxycarbonyl, carbamoyl, N—(C₁₋₆ alkyl) carbamoyl andN,N-di-(C₁₋₆ alkyl) carbamoyl.
 3. A compound according to claim 1,wherein R¹ is selected from carboxy and C₁₋₆ alkoxycarbonyl.
 4. Acompound according to claim 1, wherein R¹ is C₁₋₄ alkoxycarbonyl.
 5. Acompound according to claim 1, wherein R¹ is methoxycarbonyl.
 6. Acompound according to claim 1, wherein R^(2a) and R^(2b) areindependently selected from hydrogen, hydroxy, C₁₋₆ alkoxy and C₁₋₁₂alkanoyloxy, or R^(2a) and R^(2b) together represent oxygen.
 7. Acompound according to claim 1, wherein R^(2a) and R^(2b) areindependently selected from hydrogen, hydroxy and C₁₋₄ alkoxy, or R^(2a)and R^(2b) together represent oxygen.
 8. A compound according to claim1, wherein R^(2a) and R^(2b) together represent oxygen.
 9. A compoundaccording to claim 1, wherein R^(3a) and R^(3b) are independentlyselected from hydrogen; hydroxy; C₁₋₆ alkoxyl; C₁₋₁₂ alkanoyloxyl; C₁₋₆alkyl, which may be optionally substituted by a group selected fromhydroxy, C₁₋₆ alkoxy and C₁₋₁₂ alkanoyloxy; C₁₋₁₂ alkanoyl; carboxy andC₁₋₁₂ alkoxycarbonyl; or R^(3a) and R^(3b) together represent oxygen.10. A compound according to claim 1, wherein R^(3a) and R^(3b) areindependently selected from hydrogen; hydroxy; C₁₋₄ alkyl, which issubstituted by a group selected from hydroxy and C₁₋₄ alkoxy; C₁₋₆alkanoy; carboxy and C₁₋₆ alkoxycarbonyl.
 11. A compound according toclaim 1, wherein R^(3a) and R^(3b) are independently selected fromhydroxy, hydroxymethyl, C₁₋₄ alkanol and carboxy.
 12. A compoundaccording to claim 1, wherein one of R^(3a) and R^(3b) is hydroxy andthe other is formyl.
 13. A compound according to claim 1, wherein adouble bond is present between C8 and C9.
 14. A compound according toclaim 1, wherein double bonds are present between C7 and C8 and betweenC9 and C10. 15.8-formyl-8,9-dihydroxy-5-oxo-8,9-dihydro-5H-carbazole-1-carboxylic acidmethyl ester, which is coproverdine, and pharmaceutically acceptablesalts thereof according to claim
 1. 16. A pharmaceutical preparationwhich contains as active ingredient a compound according to claim 1, ora pharmaceutically acceptable salt thereof.
 17. A method for thetreatment of lung cancer, prostate cancer, colon cancer, leukemia, ormelanoma in a mammal, comprising administering to the affectedindividual an effective amount of a compound of formula (I);

wherein the dotted line represents an optional double bond, with theproviso that at least one single bond is present between C7 and C10; R¹is selected from hydrogen: C₁₋₁₂ alkyl, which may be optionallysubstituted by a group selected from hydroxyl, C₁₋₁₂ alkoxy, C₁₋₃₀alkanoyloxy, optionally substituted C₇₋₁₁, aroyloxy, optionallysubstituted C₈₋₁₆ aralkanoyloxy, halogen, optionally substituted C₆₋₁₀aryl, amino, mono-(C₁₋₁₂ alkyl)amino and di-(C₁₋₁₂ alkyl)amino:optionally substituted C₆₋₁₀ aryl; carboxy; C₁₋₃₀ alkoxycarbonyl;optionally substituted C₇₋₁₁ aryloxycarbonyl; optionally substitutedC₈₋₁₆ aralkyloxycarbonyl; carbamoyl; N—(C₁₋₁₂ alkyl)carbamoyl andN,N-di-(C₁₋₁₂ alkyl)carbamoyl; R^(2a) and R^(2b) are independentlyselected from hydrogen, hydroxy, C₁₋₁₂ alkyl, C₁₋₃₀ alkanoyl, optionallysubstituted C₇₋₁₁ aroyl, optionally substituted C₈₋₁₆ aralkanoyl, C₁₋₁₂alkoxy, C₁₋₃₀ alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy andoptionally substituted C₈₋₁₆ aralkanoyloxy, with the proviso that thesubstituent R^(2b) is absent if a double bond is present between C7 andC8; or R^(2a) and R^(2b) together represent oxygen; R^(3a) and R^(3b)are independently selected from hydrogen; halogen; hydroxy; amino;mono-(C₁₋₁₂ alkyl)amino; di-(C₁₋₁₂ alkyl)amino; C₁₋₁₂ alkoxy; C₁₋₃₀alkanoyloxy; optionally substituted C₇₋₁₁ aroyloxy, optionallysubstituted C₈₋₁₆ aralkanoyloxy; C₁₋₁₂ alkyl, which may be optionallysubstituted by a group selected from hydroxy, C₁₋₁₂ alkoxy, C₁₋₃₀alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy, optionallysubstituted C₈₋₁₆ aralkanoyloxy, halogen, optionally substituted C₆₋₁₀,aryl, amino, mono-(C₁₋₁₂ alkyl)amino and di-(C₁₋₁₂ alkyl)amino;optionally substituted C₆₋₁₀ aryl; C₁₋₃₀ alkanoyl, optionallysubstituted C₇₋₁₁ aroyl; optionally substituted C₈₋₁₆ aralkanoyl;carboxy; C₁₋₃₀ alkoxycarbonyl; optionally substituted C₇₋₁₁aryloxycarbonyl; optionally substituted C₈₋₁₆ aralkyloxycarbonyl;carbamoyl; N—(C₁₋₁₂ alkyl) carbamoyl and N,N-di-(C₁₋₁₂ alkyl) carbamoyl,with the proviso that the substituent R^(3b) is absent if a double bondis present between C9 and C10; or R^(3a) and R^(3b) together representoxygen; and R⁴ is selected from hydrogen, C₁₋₁₂ alkyl, C₁₋₃₀ alkanoyl,optionally substituted C₇₋₁₁ aroyl and optionally substituted C₈₋₁₆aralkanoyl; or a pharmaceutically acceptable salt thereof.
 18. Acompound of formula (I):

wherein: the dotted line represents an optional double bond, with theproviso that at least one single bond is present between C7 and C10; R¹is selected from C₁₋₁₂ alkyl, which may be optionally substituted by agroup selected from hydroxyl, C₁₋₁₂ alkoxy, C₁₋₃₀ alkanoyloxy,optionally substituted C₇₋₁₁, aroyloxy, optionally substituted C₈₋₁₆aralkanoyloxy, halogen, optionally substituted C₆₋₁₀ aryl, amino,mono-(C₁₋₁₂alkyl)amino and di-(C₁₋₁₂ alkyl)amino; optionally substitutedC₆₋₁₀ aryl; carboxy; C₁₋₃₀ alkoxycarbonyl; optionally substituted C₇₋₁₁aryloxycarbonyl; optionally substituted C₈₋₁₆ aralkyloxycarbonyl;carbamoyl; N—(C₁₋₁₂ alkyl)carbamoyl and N,N-di-(C₁₋₁₂ alkyl)carbamoyl;R^(2a) and R^(2b) are independently selected from hydrogen, hydroxy,C₁₋₁₂ alkyl, C₁₋₃₀ alkanoyl, optionally substituted C₇₋₁₁ aroyl,optionally substituted C₈₋₁₆ aralkanoyl, C₁₋₁₂ alkoxy, C₁₋₃₀alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy and optionallysubstituted C₈₋₁₆ aralkanoyloxy, with the proviso that the substituentR^(2b) is absent if a double bond is present between C7 and C8; orR^(2a)and R^(2b) together represent oxygen; R^(3a) and R^(3b) areindependently selected from hydrogen; halogen; hydroxy; amino;mono-(C₁₋₁₂ alkyl)amino; di-(C₁₋₁₂ alkyl)amino; C₁₋₁₂ alkoxy; C₁₋₃₀alkanoyloxy; optionally substituted C₇₋₁₁ aroyloxy; optionallysubstituted C₈₋₁₆ aralkanoyloxy; C₁₋₁₂ alkyl, which may be optionallysubstituted by a group selected from hydroxy, C₁₋₁₂ alkoxy, C₁₋₃₀alkanoyloxy, optionally substituted C₇₋₁₁ aroyloxy, optionallysubstituted C₈₋₁₆ aralkanoyloxy, halogen, optionally substituted C₆₋₁₀,aryl, amino, mono-(C₁₋₁₂ alkyl)amino and di-(C₁₋₁₂ alkyl)amino;optionally substituted C₆₋₁₀ aryl; C₁₋₃₀ alkanoyl, optionallysubstituted C₇₋₁₁ aroyl; optionally substituted C₈₋₁₆ aralkanoyl;carboxy; C₁₋₃₀ alkoxycarbonyl; optionally substituted C₇₋₁₁aryloxycarbonyl; optionally substituted C₈₋₁₆ aralkyloxycarbonyl;carbamoyl; N—(C₁₋₁₂ alkyl) carbamoyl and N,N-di-(C₁₋₁₂ alkyl) carbamoyl,with the proviso that the substituent R^(3b) is absent if a double bondis present between C9 and C10; or R^(3a) and R^(3b) together representoxygen; and R⁴ is selected from hydrogen, C₁₋₁₂ alkyl, C₁₋₃₀ alkanoyl,optionally substituted C₇₋₁₁ aroyl and optionally substituted C₈₋₁₆aralkanoyl; or a pharmaceutically acceptable salt thereof.
 19. Acompound according to claim 18, wherein R^(2a) and R^(2b) areindependently selected from hydrogen, hydroxy, C₁₋₆ alkoxy and C₁₋₁₂alkanoyloxy, or R^(2a) and R^(2b) together represent oxygen.
 20. Acompound according to claim 18, wherein R^(2a) and R^(2b) areindependently selected from hydrogen, hydroxy and C₁₋₄ alkoxy, or R^(2a)and R^(2b) together represent oxygen.
 21. A compound according to claim18, wherein R^(2a) and R^(2b) together represent oxygen.
 22. A compoundaccording to claim 18, wherein R^(3a) and R^(3b) are independentlyselected from hydrogen; hydroxy; C₁₋₆ alkoxy; C₁₋₁₂ alkanoyloxy; C₁₋₆alkyl, which may be optionally substituted by a group selected fromhydroxy, C₁₋₆ alkoxy and C₁₋₁₂ alkanoyloxy; C₁₋₁₂ alkanoyl; carboxy andC₁₋₁₂ alkoxycarbonyl; or R^(3a) and R^(3b) together represent oxygen.23. A compound according to claim 18, wherein R^(3a) and R^(3b) areindependently selected from hydrogen; hydroxy; C₁₋₄ alkyl, which issubstituted by a group selected from hydroxy and C₁₋₄ alkoxy; C₁₋₆alkanoyl; carboxy and C₁₋₆ alkoxycarbonyl.
 24. A compound according toclaim 18, wherein R^(2a) and R^(2b) independently selected from hydroxy,hydroxymethyl, C₁₋₄ alkanol and carboxy.
 25. A compound according toclaim 18, wherein one of R^(2a) and R^(3b) is hydroxy and the other isformyl.
 26. A compound according to claim 18, wherein a double bond ispresent between C8 and C9.
 27. A compound according to claim 18, whereindouble bonds are present between C7 and C8 and between C9 and C10.
 28. Apharmaceutical preparation which contains as active ingredient acompound according to claim 18, or a pharmaceutically acceptable saltthereof.